In Vitro and In Vivo Therapeutics of Double-Layered Hydrogels

Double-layered hydrogels are organized into different nanostructured layers and are the preferred material for various in vitro and in vivo therapeutic applications. Hydrogels are extensively employed in several domains, such as water treatment and biomedicine. Because of hydrogels' unique potentials like their tissue resemblance and ease of processing, significant progress is achieved in these domains. However, based on a thorough examination of hydrogel microstructures, it is difficult for conventional homogeneous hydrogels to concurrently address various demands due to the growth of in vitro and in vivo necessities in controlled drug delivery, cartilage repair, cell encapsulation, and other utilities. Thankfully, research on heterogeneous dual-layered hydrogels has developed and is now a remarkable area of hydrogel engineering. This review abridged the current developments in multi-layered hydrogels according to their structural design, fabrication techniques, and recent experimental findings along with special attention to the therapeutic applications of double-layered hydrogels. The report concluded by discussing the challenges in the design of double-layered hydrogels and pointed out a new direction of 3D printing, which may offer a new approach to designing double-layered hydrogels and expand the range of in vitro and in vivo therapeutic studies.